The present invention relates to an improved key-top holder in a push button switch, and more particularly, to an improved key-top holder made of an elastic or a resilient material for a push button switch, applicapable to a small-size apparatus such as a desk-top calculator, an electronic cash register or an electronic calculator.
Conventionally, electrical switches made of a conductive rubber (an elastomer) are known as disclosed in U.S. Pat. No. 3,699,294 issued on Oct. 17, 1972, entitled "KEYBOARD, DIGITAL CODING, SWITCH FOR DIGITAL LOGIC, AND LOW POWER DETECTOR SWITCHES". Also, a push button comprising a resilient body having a snaping and tilting wall of a mesa shape is known as disclosed in U.S. Pat. No. 3,932,722 issued on Jan. 13, 1976, entitled "PUSH BUTTON BODY FOR A PUSUBUTTON SWITCH PROVIDING SNAP-ACTION OF THE SWITCH".
For example, a push button as shown in FIGS. 1(a)-1(c) for a push button switch has been developed by the present applicant. A push button 1 for a push button switch has a projection 4 at the center part of the push button 1. A conductive rubber 9 is provided on the projection 4 so as to close electrical contacts on a base (not shown). An installment support member 7 is mounted on the base. When the push element or key top support section 10 of the push button 1 is depressed via a key-top (not shown), the projection 4 is moved downward so as to force the conductive rubber 9 to be engaged with the electrical contacts on the base.
According to the movement of the projection 4, the shape of the thin walls 5 and 6, supporting the projection 4, are changed. As the shape of the push button 1 changes successively, as shown in FIGS. 1(a)-1(c), the shape of the thin walls 5 and 6 are also changed as shown and are returned to their original shape (position) when the depressing force is released.
In the push button construction, as shown in FIGS. 1(a)-1(c), if many switching movements are repeated, for example thousands of times, the push button switch 1, made of an elastic rubber, will crack. For example, sections a and b of FIG. 1(a) may crack. This is because, although the length of the wall 5 is short, the distance through which the wall 5 moves is considerably longer and the wall is thus subject to snapping at sections a and b.